Electrical control system



Dec. 7, 1943. H- s JONES 2,335,943

ELECTRICAL CONTROL SYSTEM Filed Oct. 16, 1941 4 Sheets-Sheet l INVENTOR.

HARRY S. JONES OR'NEY I- :c. 7, 1943. H. s. JONES 2,335,943

ELECTRICAL CONTROL SYSTEM Filed Oct. 16, 1941 4 Sheets-Sheet 2 INVENTOR.

HARRY S. JONES AT RNEY Dec. 7, 1943. H. s. JONES 2,335,943

ELECTRICAL CONTROL SYSTEM Filed Oct. 16, 1941 4 SheetsShee't 3 FIGS.

INVENTOR.

riw zf HARRY S. JONES H. S. JONES ELECTRICAL CONTROL SYSTEM Dec 7, 1943.

Filed Oct. 16, 1941 4 Sheets-Sheet 4 L llll llllll INVENTOR.

HARRY S. JONES y O'RNEY Patented Dec. 7, 1943 gamm ELECTRICAL CONTROLSYSTEM Harry S. Jones, Washington, D. 0., assignor to The BrownInstrument Company, Pa., a corporation of Pennsylvania Philadelphia,

Application October 16, 1941, Serial No. 415,253

Claims.

The present invention relates to control instruments and moreparticularly to electrical control instruments that may be provided withfollow-up and/ or reset.

In the control of various condition such as temperature, pressure orflow the primary measuring element is made as sensitive as possible inorder that it will respond accurately to minute changes in thecondition. This usually means that there is very little power producedby the measuring element for the operation of any control apparatus. Itis, accordingly, highly desirable that the control mechanism be soconstructed that a minimum of power is required to operate it.Furthermore, if the measuring element is very sensitive some auxiliaryforce must be used to operate the control valve as well as the parts ofthe control mechanism which serve to provide the follow-up and resetfunctions of the instrument.

To this end I have developed an electrical control instrument which hasa minimum of parts moved directly by the measuring element, each ofthese parts being very light in weight. It is an object of the inventionto provide an electrical control system that may be operated in apositive manner without imposing an appreciable load on the measuringelement. It is a further object of the invention to provide anelectrical control system that is compact in form and one that iscapable of responding quickly and accurately to any changes in thecondition being controlled. It is a further object of the invention toprovide an electrical control instrument which will quickly bring thevalue of a condition to some desired point with a minimum of hunting andaccurately maintain the condition at that point.

Another object of the invention is to provide a control instrument inwhicha very small flow of current through a, pair of movable contactsmay be used to control a large fiow of current in a control circuit,whereby there will be no sparking at the contacts.

In carrying out the invention there is employed a light contact memberthat is moved by the primary measuring element. This contact serves toclose or open an electric circuit that may include an electronicamplifier. The electric circuit operates, either directly or through arelay, to set into operation a control motor and the follow-up and resetmechanisms of the system, when the latter are used.

The various features of novelty which characterize this invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,however, its advantages and specific objects obtained with its use,reference should be had to the accompanying drawings and descriptivematter in which is illustrated and described a preferred embodiment ofthe invention.

Of the drawings:

Fig. 1 is a view of an instrument embodying one form of control circuitand having a fluid controlled follow-up and reset,

Fig. 2 is a view of an instrument using a control circuit different fromthe one in Figure 1,

Fig. 3 is a view of an instrument similar to Figure 1 including acircuit with an electronic amplifier,

Fig. 4 is a view of a modified motor control circuit for use with Figure3,

Fig. 5 is a view of an instrument, also having an electronic amplifier,and with an electrical follow-up,

Fig. 6 is a view of an instrument having an electronic amplifier and tobe used as an on-ofi' controller, and

Fig. 7 is a view of an instrument for proportional control and having areversible motor follow-up.

Referring first to Fig. 1 wherein one form of my invention is shown, byway of example, as controlling the temperature of a furnace I that issupplied with some temperature changing fluid through a pipe 2, the flowof which is regulated by a motor driven valve 3. The temperature of thefurnace is measured by a bulb 4 which is filled with a temperatureresponsive liquid and which is connected by a capillary 5 to one end ofa Bourdon tube 6 that is mounted in an instrument casing, a portion ofwhich is shown at 1. As the temperature of the furnace varies the outerend of the Bourdon tube will move to the right or to the left andthrough a lever mechanism, presently to be described, will serve toraise or lower the link 8.

Movement of the outer end of the Bourdon tube 6 is imparted to a link 9,through a connection ID, to the bell crank lever ii that is in turnfastened to a pivoted shaft [2. As the lever moves around the shaft l2it moves one end of a floating lever N that is pivoted at l5 andconnected to the lever ll by a link l6. As the Bourdon tube expands andcontracts the link 8 is raised and lowered.

The control point of the instrument, or the temperature which theinstrument will tend to maintain in the furnace i, can readily be variedby moving the right hand end of the lever l6.

-'Ihis is accomplished by raising and lowering the pivot point l5 thatis attached to a lever i1, pivoted at l8. The right arcuate edge of thelever I1 is provided with gear teeth that are driven through a geartrain l9 from a knob 20. Therefore, as the knob is rotated the lever l1will move pivot l5 upwardly and downwardly to impart the same type ofmovement to the member 3 l.

link 8 that is imparted to it by the Bourdon tube. The lever I1 isprovided with a pointer 2| which serves to cooperate with a chart, notshown, to indicate the control point of the instrument.

3 There may also be mounted on the shaft |2 a pen and pen arm, notshown, to cooperate with the chart in order to produce a record of thevalue Of the temperature of the furnace lengthwise movement of the link-8 serves to move a contact 22 around its pivot 23 into and out ofengagement with a stationary contact 24. This is accomplished by meansof a pin 25 which extends from one arm of a lever 26 into the path ofmovement of the contact 22. The lever 26 is pivoted at 21 and has thelower end of link 8 attached to one of its arms. Contact 22 is normallybiased in a counter-clockwise direction.

The contacts 22 and 24 may also be moved relative to each other in onedirection by the action of a spring 28 and in the other direction by theaction of a solenoid 29 on its core 30. To this end a solenoid isattached to the outside of a cup shaped casing member 3| against theinside of which the left end of the spring 28 bears. The right end ofthe spring 28 bears against a socket formed in a plate 32 that serves asthe end wall of a bellows 33 whose open end is attached to a support 34along with the open end of the member 3|. Also attached to this support34 is one end of a bellows 35 which serves to form, with the bellows 33,a chamber 36. This chamber is in communication with a similar chamber 31by means of a pipe 38 that is provided with an adjustable restriction39. The chamber 38 is formed of a large bellows 40 and a small bellows4| that are attached to a support 43 and which are in opposing relationwith the bellows 33 and 35 respectively. The bellows 40 is protected bya cup shaped casing member 44 similar to the Each of the chambers 36 and31 along with the pipe 38 are filled with a liquid that can move backand forth between the two at a rate depending upon the adjustment of therestriction 39. I

The inner ends of bellows 35 and 4| are joined by a rod 45 that isprovided with a projection 46. This projection bears against the leftedgebf a lever 41 pivoted at 48. The right edge of the lever 41 actsthrough pin 49 on a lever 50 that is supported for movement at its upperend around a pin and which supports on its lower end the lever 26. Theamount of movement imparted to the lever 58 for a given movement of thelever 41 I can be varied by raising and lowering the pin 49 which ismounted on the lower end of lever 52. This lever 52 is pivoted to amovable support 53.

The contacts 22 and 24 form part of a circuit including a source ofelectric current 54, solenoid 29 and a solenoid 55. Another circuitforms part of the control system and includes the source of current 54,a slideable contact 56 which is movable along the resistance 51 and asolenoid 58. Cores 59 and 60 of the solenoids and 58 respectively serve,upon changes in energization of these two solenoids, to move a contact6| into engagement with either a, stationary contact 62 or a stationarycontact 63. Engagement of the contact 6| with either of the othercontacts energizes a reversible motor 64 for rotation in one directionor the other. This motor is supplied with current through the lines Land As the motor rotates it adjusts the opening of valve 3andsimultaneously shifts the contact 56 along the resistance 51.

In a description of this operation of this instrument the various partswill be described as if they moved sequentially, but it must beremembered that the movements of the various parts take placecontinuously and contemporaneously so that the control impulse set up bythe instrument as a result of a change in the value of the conditionbeing measured is almost immediately applied to the control valve. Forpurposes of description it may be assumed that the temperature of thefurnace 4 has increased so that the valve 3 should be closed to supply asmaller amount of the temperature varying fiuid'through the pipe 2. Asthe temperature of the furnace increases the outer free end of theBourdon tube will move toward the right and acting through link 9 andlevers H and 4, will move the link 8 downwardly. This movement willcause the pin 25 to move to the right away from the contact 22 and thatcontact will move under normal bias into engagement with the contact24.A circuit will, therefore, be closed through the two contacts, thebattery 54, solenoid 55 and solenoid 29. This operation produces tworesults; the first of which energizes the solenoid 55 so that the core59 will be moved downwardly and the contact 6| will be brought intoengagement with the contact 63. This energizes the motor 64 for rotationin a direction to close the valve 3 and to simultaneously move thecontact 56 to the left along resistance 51. The movement of the contact56 cuts some of the resistance 51 out of the circuit and, therefore,produces a greater energization of the solenoid 58. This continues untilthe solenoid is sufliciently energized to move contacts 6| and 63 out ofengagement with each other to stop motor 64 and the adjustment of thevalve 3. The second result of the engagement of contacts 22 and 24 is toenergize the solenoid 29. This produces a movement of the core 38 to theleft against the force of spring 28 to elongate bellows 33 and, throughthe liquid in chamber 36, elongate bellows 35. As the bellows 35 iselongated it moves rod 45 to the left and pin 46 acting through levers,41 and 58 serves to move the pin 25 to the left to disengage contacts22 and 24.

This follow-up movement is provided to prevent er compression than thatin chamber 36, it will tend to flow through the pipe 38 at a ratedepending upon the adjustment of restriction 39. This will permit thebellows 35 to contract and the bellows 4| to elongate to their normallengths and will permit the pin 46 to return to its initial position.Such action more or less cancels out the effect of the follow-upmovement of the contact 22. This action is known as reset and serves tocompensate for load changes in the furnace by bringing the contact 22back to substantially its original position with a different opening ofthe valve 3.

If the temperature of the furnace had decreased the contact 22 wouldhave been moved out of engagement with the contact 24 to deenergize thesolenoid 55. The pull of solenoid 58 on its core 60 would then movecontact 6| into engagement with contact 62. This will energize the motor64 for rotation in direction to open valve 3 and shift contact 56 to theright to insert more of resistance '51 in the circuit until the pull ofsolenoid55 equals that of-solenoid 58. When this occurs the motorcircuit will be opened. The same movement of contact 22 toward the leftdeenergizes solenoid 29 so that spring 28 can move the mechanismcontrolled thereby to the accepts right. The spring 28 thus serves toprovide the follow-up movement and to bring contacts 22 and 24 intoengagement again.

The operation is such that the contacts 22 and 24 are continualiy'movedinto and out of engagement with each other so that there is any averageexcitation value of solenoids 29 and 88. This average is decreased orincreased depending upon whether the temperature of the furnace I hasincreased or decreased respectively and, therefore, an adjustment of thevalve 3 is procured.

It will be seen that the only parts actually moved as a result ofmovement of the Bourdon tube are very light levers connecting that tubeto the lever 28. These serve to move the contact 22 which carries a verysmall current and which is freely mounted on its pivot. As a result ofthis, contacts in a second circuit carrying a larger current areimmediately closed so that a response of the motor 84 to changes oftemperature in the furnace is practically instantaneous and. due to thefollow-up in the lever system, there is no tendency for cycling aroundthe control point to occur. This quick operation of the mechanism with apractically negligible load on the Bourdon tube gives a highly effectiveand sensitive control system.

The system shown in Fig. 2 is substantially the same as that disclosedin Fig. 1 except that in this case the motor 84 is operated directlyfrom movement of the contact 22. With this embodiment of the inventionas the temperature of the furnace decreases contact 22 will be movedinto engagement with a stationary contact 65 and as the temperatureincreases the contact 22 will be moved into engagement with a secondstationary contact 88. These contacts 85 and 68 are directiy connectedin the field circuits of the motor 84. As the motor rotates it willadjust the valve 8 in a manner previously described and willsimultaneously shift a contact 81 along a variable resistanee 68 toeither increase or decrease the energization of the solenoid 29 as thecase may be, in order that a proper follow-up action may be imparted tothe contact 22. If, for example, 22

. moved into engagement with contact 65 then the energization ofsolenoid 29 should be decreased in order for the spring 28 to shift theparts in a direction to separate the contacts 22 and 88. On the otherhand, if 22 should move into engagement with contact 68 the energizationof 29 should be increased to move core 30 against the force of thespring 28 so that the rod 45 and proiection 46 will move to the left topermit separation of the two contacts.

It will be seen that in this embodiment of the invention there is showna means to close an electrical circuit in response to a deviation in thevalue of the condition being controlled and to have these circuits actswithout any further load upon the measuring element to operate both thecontrol valve and to give follow-up and reset action to the movablecontact. This embodiment of the invention differs from that of Figure 1in that the contact 22 is not being continually moved. In this figurethe contact 22 is moved into engagement with either 85 or 68 when thecondition changes and is moved back to its neutral position by thefollow-up mechanism. In- Figure 1 either solenoid 29 or spring 28 wascontinually acting on the apparatus, while in Figure 2 solenoid 29 andspring 28 can be made to balonce each other by properly adjustingcontact 81 along resistance 88.

Inl'igure8 thereisshownanembodimentof the invention using an electronictype of ampliiier. There is also shown a slightly diflerentmechanism forobtaining the follow-up and reset movementsof the contact 22. In thisembodiment the space between the cup-shaped member 8| and the bellows I2is iiiled with liquid and the space is placed in communication with theinterior of a bellows 89 by a pipe 18. The bellows is protected by acasing 1| and has attached to its movable lower end a solenoid core 12.This core, along with the bellows bottom wall, is urged downwardly by aspring 18.

In this case the contact 22 is connected by a wire 14 with a resistance18 and a tap on the secondary coil of a transformer 18. 'The primary ofthe transformer is connected to a suitable power line indicated by linesL and L Wire 14 is also connected with the control grid 18 of anelectronic tube 19. This tube is provided with a heating filament 89that is connected to a separate, small transformer secondary. The tubeis also provided with a cathode 8| that is connected to the transformer,a screen grid 82 and an anode or plate 88'. The screen grid and plateare connected together and by wire 81 to two solenoids I4 and that arein parallel with each other and in series with the plate. The othersides of the solenoid are connected by wire 11 to a tap on thetransformer secondary. The solenoids 84 and 85 are shunted by acondenser 88. The contact 22 is adapted to move into and out ofengagement with a stationary contact 88 that is directly connected withanother tap on the transformer.

Control motor 84 is adapted to be energized for rotation in onedirection or the other by engagement of a contact MA with on of thecontacts I 82 or 83. Contact SIA is adapted to be moved around its pivotin a counterclockwise direction into engagement with the contact 82 by acore 89 of solenoid 85 but is normally biased in a clockwise directionby a spring 98. The upper end of spring 99 is connected to an arm 9ithat is driven by the motor to change the tension of the spring as thecontrol valve 3 is being. adjusted.

In describing the operation of this embodiment of the invention it maybe assumed that the left end of the secondary winding of transformer 18is more positive than the right end, as will occur once each cycle ofthe current. At this time if contacts 22 and 88 are separated thecontrol grid is more negative than the cathode 8i so that no flow ofelectrons can take place from cathode to plate 83.. Therefore thecircuit through solenoids 84 and is open. When there is, for example, adecrease in the temperature of the furnace i the various parts of theinstrument will move to bring contact 22 into engagement with thecontact 88. This will complete a circuit from the right end of thetransformer secondary through resistance 15, wire 14, contacts 22 and 88back to the transformer winding. The eil'ect of this is to make thepotential of th control grid more positive with respect to the oathodeso that current may flow through the tube 19 and energize solenoids 84and 85.

Energization of the solenoid 84 will serve to move its core 12 upwardlyagainst the force of spring 18 to compress bellows 69 and the fluid init, pipe 18 and the chamber formed between member 3i and bellows 33.This operates through the mechanism described in detail in connectionwith Figure 1 to give a follow-up movement to contact 22. In thisembodiment, as in Figure 1, the contacts 22 and 88 are continually movedinto and out of engagement with each other with the average time ofengagement varying with the changes in the temperature of the furnace.

Energization of the solenoid 85 serves to move core 89 downwardlyagainst the force of spring 90. This brings contact BIA into engagementwithcontact 92 to energize motor 64 for rotation in a direction to openthe control valve Sand let more of the heating fluid flow through pipe 2to the furnace. This same operation of the motor will move lever 90clockwise to increas the tension of spring 90 and separate contacts BIAand 62. Thus the valve 3 will be positioned in accordance with the valueof the condition.

Condenser 88 serves to iron out the impulses of current supplied to thesolenoids from the electronic tube I9.

In Figure 4 there is shown a modified form of circuit for controllingthe motor 94 that is to be used with the electronic amplifier of Figure3. In this figure there is shown a balanced bridge, two opposite legs ofwhich consist of variable resistances 92 and 93. These resistances maytake the form of lamps, in whichcase the filaments may desirably be madeof carbon. In this case as more or less current is passed through thelamps their resistance will be changed to un balance the bridge. A thirdarm of'the bridge consists of a fixed inductance 94 while the fourth armof the bridge consists of a variable inductance 95, the inductance ofwhich, is changed to rebalance the bridge upon the occurrence of anunbalance thereof.

The bridge network is supplied with current, varying in accordance withthe temperaturebeing measured, from the electronic amplifier of Figure 3through wires I1 and 81. These wires are connected to the transformersecondary and the plate 93 of tube I9 respectively as shown in Figure 2.Inserted in the wire 81 is the solenoid coil 84 which is shunted by thecondenser 86.

The unbalance of the bridge network is detected by a galvanometer 90whose deflecting pointer is provided with a contact BIB. This contact isadapted, upon unbalance of the bridge, to be brought into engagementwith one-of contacts 62 or 63 to energize motor 94. The motor, as in thepreviously described embodiments, serves to adjust the control valve 3.Motor 64, in this case, also adjusts a core 91 of the variableinductance Upon the occurrence of a change in temperature of the furnaceI the contacts 22 and 88 are brought into engagement in a manner alreadydescribed. This acting through the electronic amplifierserves to close acircuit which includes wires 81 and 88 and those parts connectedthereto. This serves to energize solenoid 84 in a manner previouslydescribed to give a follow-up movement to the contact 22. Simultaneouslycurrent is supplied. to the bridge circuit in an amount proportional tothe temperature change to light the lamps 92 and 93. Due to the type offilaments that are used in the lamps their resistance will changecorrespondingly and the bridge In Figure 5 there is disclosed anotherembodiment of the invention in which a solenoid energized from anelectronic amplifieris-used to give the follow-up movement of thecontact 22 directly and in which manual reset is provided. An electronicamplifier generally similar to that of Figure 3 is used and anelectrical relay circuit specifically difierent from that of Figure 3 orFigure 4 is used to control motor 64.

The contact moving mechanism is shown diagrammatically in Figure 5 butvarious parts have been given the same reference numerals that they hadin previously described figures. The levers 50 and 41 are biased to theleft by a spring 98. In this manner a pin 99 of the lever 41 ismaintained in engagement with one edge of a wedge shaped member I00.This member is mounted on a lever IOI so that it can be raised orlowered to vary the distance between the pin 99 and a second pin I02 onone end of a stem I03 of a solenoid armature I04. Cooperating with thearmature I09 is a solenoid I05 through the center of which the stem I03projects. Attached to the right end of the solenoid is a guideway I05that receives an enlargement I01 on the stem to guide the same as itreciprocates. Surrounding the stem I 03 and received between thearmature I04 and the left I end of the solenoid is a spring I08 whichacts to normally bias the armature and its associated mechanism to theleft. The force of the spring is one side of the line and the plate I I2is connected will be unbalanced. This unbalance will be de- 3 and willsimultaneously shift the core ofthe inductance to rebalance the bridgecircuit and thereby stop the adjustment of the valve 3 when it is openedthe proper amount.

to one terminal of solenoid I05, whose other terminal is connected tothe other side of the line. A condenser H3 is shunted across thesolenoid. The amplifying section of the tube is also provided with ascreen grid IM that is connected to the plate and a control grid I I5that is connected by a wire IIB through a pairof current limitingresistors A and B to a contact I II that cooperates with contact 22. Acondenser H8 is shunted across the two contacts 22 and I II, Therectifier section of tube H0 is provided with a cathode I I9 that isconnected to one side of the line, and a plate I20 that is connectedthrough a condenser.

I2I to the other side of the line. Paralleling the condenser I2I is aresistance C that is connected between the resistances A and B in wireH6 and to one terminal of the condenser I I9.

The relay that is used to control motor 64in this embodiment is actuatedfrom the stem I03 of the armature I04 in response to movement thereof.This movement operates a pilot relay that in turn operates a load relayin the circuit of motor 64.

The left end of stem- I03 carries a contact I22 that is moved therewithbetween a stationary conductor I23 and a variabl resistance I24. Theends of the resistance are connected in a closed circuit to the ends ofa similar resistance I25 and the connecting wires have in them pilotrelay coils I26 and I2I respectively. To energize the circuit theconductor I23 is connected to a transformer secondary I28 and from thereto -a movable contact I29 that bears against the resistance I25. Theseparts in effect form a bridge circuit which upon movement of contact I22will cause more or less current to'flow through one of the pilot coilsI26 or I2'I than through the other. The

coils are provided with a responsive mechanism (not shown) that operatesto throw a switch arm I36 into engagement with one of the contacts I3Ior I32 to control the energization of a pair of load relay coils I33 andI34. These coils are ener- Y gized upon actuation of the switch I30 by atransproper direction, to adjust valve 3 and simultaneously shiftscontact I23 along resistance I25 in a direction to produce equalenergization of the coils I26 and I21. This operation opens the variousswitches and stops rotation of motor 64.

In the operation of the embodiment of Figure 5 on one half cycle of thecurrent supplied through lines L and L electrons can flow through therectifier section of the tube -IOI from the cathode II! to plate I tocharge condenser I2I, The subsequent discharge of the condenser I2Ithrough resistance C serves to place a charge on the condenser H8. Sincethe cathode III is grounded-through the contact 22, the charging ofcondenser H8 serves to make grid II5 negative with respect to cathodeIII. Therefore on the next half cycle if contacts 22 and I I1 are not inengagement with each other no current can flow in the plate circuit ofthe tube. If, however, due to the increase in the temperature of thefurnace the contact 22 is brought into engagement with contact 1 thecondenser III! will discharge through the contacts to bring thepotential of the control grid II5 substantially to the value of that ofthe cathode III. Current can, therefore, flow through the tube, and acircuit will be completed from line H cathode III, plate II2, solenoidI05 back to line L The solenoid will, therefore, be energized inresponse to an increase in temperature of th furnace I. The condenserII3 serves to smooth out the ripples of the currents supplied by thevacuum tube IIO.

Energization of solenoid I05 serves two purposes. First the armature I04along with its stem I03 is moved to the right against the force ofspring I08 and operates through the lever system to separate contacts 22and H1 in a follow-up movement. This same movement of the armatureserves to shift contact I22 to the right along resistance I24 tounbalance the circuit including the resistance I25 and the pilot relaycoils I26 and I21. The relay coil I 26 will, therefore, be energized toa greater extent than coil I21 and switch arm I30 will be moved upwardlyinto engagement with contact I3I. This serves to energize the load relaycoil I33 so that its armature will move the switch arm 6IC to the leftinto engagement with contact 63. This energizes the motor 64 forrotation in a direction to close the valve 3 and reduce the supply ofheating fluid to the furnace so that the temperature will return tonormal. Rotation of a motor 64 will also shift the contact I25 to theleft to rebalance the bridge circuit so that coils I26 and I21 will beenergized the same amount. At the time the energization of these coilsis equal the switches I30 and 6IC will be opened to stop the rotation ofthe motor. The valve 3 at this time will be opened an amount snflicientto supply enough heating fluid to maintain the temperature of thefurnace constant.v If the increase in temperature was due to a decreasein load the operation of the system disclosed will probably not bringthe temperature back to the control point since the system is providedwith only a follow-up action. In order to compensate for the change inload inthe furnace the member I00 may be shifted to vary the distancebetween pins I02 and 99. This, in effect, changes the length of armaturestem I03 and resets the contact 22 to a new position for the new load onthe furnace. With this embodiment, as in the previous embodiments of theinvention, the contact 22 will be continuously moved between opened andclosed positions and a change in the value of the condition varies theaverage time that the contact is out of or in engagement with thecontact II 1.

It will be seen that this embodiment of the invention uses the solenoidwhich is energized from the vacuum tube to directly give a follow-upmovement to the movable contact. This solenoid also operates the relaycircuit of the system so that the control motor will be run in theproper direction to adjust the valve. At times when automatic reset isnot necessary to the system it may be found advisable to use this typeof mechanism rather than that disclosed in the previously describedfigures.

The embodiment of the invention disclosed in Figure 6 provides an on-oifcontrol; that is one in which the control valve is opened when thecondition is low and the control valve is closed when the condition ishigh. In this embodiment the lever 26 is mounted on a support I31 and isprovided with a projection 26A that acts through a movable pin I38 toshift the contact 22. As the pin I38 is raised andlowered more or lessmovement of the link 8 is required to separate the contacts 22 and H1.The amplifier circuit used with this embodiment of this invention isidentical with that of Figure 5 except that the solenoid I05,,in thiscase, is used to move a switch arm I39 a gainst a stationary contact I40to energize a solenoid I4I. This solenoid is the actuating member of avalve I42 in the fuel supply linegZzthe valve being normally closed by aspring and opened by the solenoid when the latter is en, gized.

,''In the operation of this embodiment the link 8 ,is connected to theleft end of the lever 26 so that an upward movement of this link inresponse to a decrease in the temperature of the furnace I will permitthe contact 22 to move into engagement with contact II1. This, inthemanner previously described, will cause energization of the solenoid I05through the electronic tube IIO to close contacts I39 and I 40. Uponclosure of this contact the solenoid MI is energized to open the valveI42 which valve remains open until such time as the temperatureincreases above normal. Thereafter the instrument will operate to lowerlink 8 and separate contacts 22 and H1. This operation will permit acurrent flow through the amplifier section of the tube III] so that thesolenoid I05 will be deenergized. Consequently the switch I39 will open,solenoid I I! will be deenergized, and the valve I42 will close underits normal spring bias. The valve will remain closed until such time asthe temperature decreases below the control point.

The embodiment of the invention shown in Figure '1 has follow-up andmanual reset such as was provided in the embodiment of Figure 5. In thiscase, however, the follow-up is obtained by means of a reversible motorwhich is energized for rotation in the proper direction in response tochanges in the temperature of the fur tween these two contacts, thesolenoid and a source of electricalenergy I45. Energization of thesolenoid serves to move a switch .arm I46 downwardly against the bias ofa spring I4I into engagement with a contact I48. A circuit is closedwhen these two contacts engage through the contacts and a transformersecondary winding I49 to the field I56 of a reversible motor II.Normally when the solenoid I44 is not energized the switch arm I46 willbe in engagement with a contact I52 to energize through a' similarcircuit motor field I53. I

Energization of the motor I5I will produce rotation of a pinion I54 thatis on the motor shaft to accomplish two purposes. First, this pinionwill rotate in a direction to shift a rod I55 having rack teeth formedon it and in mesh with, the teeth of the pinion in a direction to give afollow-up movement to the contact 22. The second .operation of thispinion I54 is to move the rod I55 so that a resistance I56 wound on itsleft end will be moved relative to a contact I51, This resistance formswith a second resistance I58, a bridge circuit that has in its armsrelay coils I59 and I66. The bridge is energized from the contact I5'Ithrough a transformer secondary winding I6I to another movable contactI62, which is movable across the resistance I58. The transformerwindings I49 and I6I are energized from a primary winding "53- that isconnected directly to the line. When one of the relay coils I59 or ISObecomes more energized than the other due to movement of rod I55 it willoperate to move the contact GID' into engagement with either contact 62or 63 to energize motor 64 for rotation. This motor adjusts the openingof the ,control valve 3 and simultaneously moves conclockwise. Thispinion shifts rod I to the right to give a follow-up movement to-thecontact 22.

coils I59 and IE0 and thereby open' the control switch for motor 64.

The contact 22 in this embodiment is also con.-

' tinually moved into and out of engagement with the stationary contactI43 as was done in some of the previously described embodiments. Itshould be noted that in each embodiment of the invention the movement ofcontact 22 is very small and that the movement of the parts of thevarious control systems which produce that movement is negligible. This,however, keeps the instrument in a nascent state so that it caninstantly respond to any changes in temperature. Such operation producesa very sensitive control instrument.

From the above description it will be seen that I have invented acontrol system which is instantly responsive to changes in the value ofa condition being measured and which can operate to immediately correctthat condition by changing the setting of the control instrumentalitiesthe proper amount to correspond to the condition change. The instrumentoperates with a very low value of voltage on the control contacts andthe circuit is completed through a very high impedance so that nosparking may occur at that point. This low voltage is sufficientlyamplified to actuate the necessary control mechanism..

Having now described this invention, what I claim as new and desire tosecure by Letters Pat- 'ent is:

1. In a control instrument, the combination of a pair of electricalcontacts, means tending at the force of said-first means, an elementmovable in response to variations in the value of a condition, mechanismoperated by said element to move one of said contacts relative to theother independently of said means to move said contacts into engagementwith each other or out of engagement with each other depending uponvariations in the value of said condition in either direction from apredetermined value, and means operated in response to engagement anddisen- 1giagement of said contacts to control said condiion.

2. In a control instrument, the combination of a pair of electricalcontacts, resilient means tending'to at all times move one of saidcontacts in one direction relative to the other, electrical meansoperative upon engagement of said contacts to move said one of thecontacts in the opposite direction relative to the other against theforce of said resilient means, an element movable in response tovariations in the value of a condition, mechanism operated by saidelement to move one of said contacts into or out of engagement with theother independently of said first two means depending upon whether thevalue of the condition is above or below a predetermined value, meansoperated upon closure of said contacts by said element to operate saidelectrical means, and means operated in one direction or the other assaid contacts are closed or opened to control the value of saidcondition.

3. In a control instrument, the combination of an element movable topositions depending upon the value of a condition, a pair of electricalcontacts, mechanism operated by said element to move said contacts intoor out of engagement with each other depending upon whether the value ofsaid condition is above or below a. predetermined value, fiuid operatedmeans acting on said mechanism independently of said element to movesaid contacts into or out of engagement with each other, resilient meansand electrical means acting in opposition to each other and on saidfluid operated means to cause the latter to move the contacts, secondelectrical means operative to control a condition varying medium, andmeans to simultaneously energize said two electrical means upon closureof the contacts.

4. In a control system, a pair of cooperating contacts, a first meanstending at all times to maintain one contact in engagement with theother, second means operative at times to oppose said first means andseparate said contacts, means operated upon closure of said contacts toenergize said second means whereby the same will open the contacts, anelement movable in response to variations in a condition, mechanismoperated by said element to move one of said con-'- tacts in a directionto supplement the action of said first-means or said second meansdepending upon whether the value of the condition is above or below apredetermined value, and control means for said condition operated tochange the value of the condition in one direction or the oppositedirection by the opening and closing of said contacts.

5. In a control system, a pair of cooperating contacts one of which ismovable, a first means tending at all times to open said contacts, asecond means opposing said first means and adapted at times to closesaid contacts, fluid operated mechanism acting between said first andsecond means and said movable contact to move the latter by operation ofthe former, said mechanism giving an independent movement to the contactdepending upon the actuation of said first and second means, an elementmovable in response to variations in a condition, connecting meansbetween said element, said mechanism, and said movable contact wherebysaid element will move said contact to supplement movement impartedthereto by said first or second means depending upon whether thecondition is above or below a predetermined value, and an electricalcircuit including said contacts and said second means to operate thelatter when said contacts close.

6. In a control instrument, the combination of a'stationary contact anda movable contact, means responsive to variations in the value of acondition to move said movable contact relative to said stationarycontact in a direction depending upon the direction of change of thecondition, fluid operated means to give a followup movement to saidmovable contact in response to a movement thereof by said responsivemeans, a plurality of motive means operable in opposite directions, anelectronic control circuit adapted to regulate the operation of saidmotive means in said opposite directions, said circuit being connectedwith said contacts and controlled to operate said motive means inopposite directions by engagement and disengagement of the same, meansactuated by one of said motive means to operate the fluid means, andmeans operated by another of said motive means to control the condition.

'7. In a control instrument, the combination of a stationary contact, amovable contact, an element movable in response to variations in thevalue of a condition to move said movable contact into or out ofengagement with said stationary contact, an electric power supplyingmember, an electronic control circuit to control the operation of saidmember, said circuit including a vacuum tube including a plate, cathodeand a grid, said member being in the plate circuit, a condenser in acircuit between the grid and cathode, means to supply direct current tocharge said condenser to supply a negative bias to said grid,connections between the terminals of said condenser and said contactswhereby upon closure of said contacts said condenser will be dischargedto permit flow of current in the plate circuit and operation of saidmember, and condition controlling means regulated through operation ofsaid member.

8. In a control instrument, an element movable in response to variationsin the value of a condition, a control member operated in one sense oran opposite sense to control said condition, means to operate saidmember in response to movements of said element comprising a vacuum tubehaving a plate, a grid and a cathode, means to supply power to saidtube, a plate circuit comprising said source of power, said cathode,said plate and said member, a grid circuit comprising said grid, acondenser and said cathode, means to supply direct current to chargesaid condenser in a manner to place a negative bias-on said grid Iwhereby no current can flow in said plate circuit,

a contact connected to each side of said condenser, means controlled bysaid element to engage or disengage said contacts whereby when saidcontacts are closed said condenser may be discharged to permit currentto flow in said plate circuit.

9. In a control instrument, a plurality of interconnected electriccontrol circuits, a single pair of contacts one of which is movable, anelement movable in response to variations in the value of a condition,mechanism operated by said element to move said movable contact into orout of engagement with the other of said pair of contacts depending uponwhether the condition is above or below a predetermined value, meansacting through said mechanism to give normally a follow-up movement inone direction to said movable contact but operable to give said movablecontact a follow-up movement in the opposite direction, motor operatedmeans normally tending to adjust the value of the condition in onedirection, but operable to adjust the value of the condition in theopposite direction, one of said control circuits operating to controlsaid motor to adjust the condition in the said opposite direction,another of said control circuits controlling said means giving thefollow-up movement, to give a follow-up movement in said oppositedirection and means operated upon engagement and disengagement of saidpair or contacts to control the operation of said electrical controlcircuits.

10. In a control instrument, the combination of a pair of contacts, oneof which is movable, responsive means to move said contacts into and outof engagement with each other in response to variations in the value ofa condition, means normally acting to adiust said condition in onedirection but operable to adjust said conditon in the oppositedirection, fluid actuated follow-up means normally acting to give saidmovable contact a follow-up movement in one direction but operable togive a follow-up movement in the opposite direction, an electric relaycircuit opened and closed by said contacts, and means operated uponclosure of said relay circuit, to operate said follow-up means to givesaid movable contact a follow-up movement in said opposite direction,and to operate said means to adjust said condition in said oppositedirection.

HARRY S. JONES.

